I have almost 80 m2, of which about 70 m2 are heated. Somehow I managed to insulate it to the level of 4-5 thousand kWh per year, and half and half of the energy comes from electricity and wood. This winter, I will probably use less than 2,000 kWh of electricity, which gives about PLN 500 + 2 m3 of wood for about PLN 300. I burn wood in a fireplace (actually a fireplace stove) with an installed coil that captures some of the heat normally escaping the chimney. In conjunction with the collector, I have "free" hot water almost all year round, and I connect the heater in the boiler to the socket only a few times a year. And to think that the previous owner used about 5 tons of coal a year 10 years ago

Importantly, a significant part of the insulation could be done very cheaply because there is a space for 15 cm of wool above the ceiling, only this would reduce the consumption by about 2 tons of coal. In old houses we have huge reserves that allow us to save, you just need to know how to use them.
Jesion40 - if I bought a house with a floor covering, I would also be interested in an air-water pump. It is a kind of a natural compound, because the low-temperature underfloor heating system boosts the COP of the pump. Then I would give up the collectors because they are competition for pumps: when the collectors are the most efficient, the pump also achieves the highest COP. For this reason, one of these devices will not be used in an optimal way. It is worth checking what are the possibilities of installing thermal insulation above the ceiling, because that is where the most heat escapes. This means that there will also be the fastest ROI.
The easiest method
estimates The return on your investment would be to determine the energy consumption of your home. The average annual temperature difference between the house and its surroundings during the heating season in northern Poland is approx. 20 degrees. If it's 0 degrees outside you can just plug in the electric heaters and see what power they will hold at 20 degrees. That power multiplied by 170
* will give the annual heat demand, and when multiplied by 2, the continuous power needed at 20 degrees frost. When counting the power for the accumulative power on the 2nd tariff, you need to use 4 (G12r) or 4.8 (G12). In the accumulative weekend tariff (G12w) at -20 degrees the power on weekdays will be 4.8 times higher than the continuous one at 0 degrees, and on Saturdays, Sundays and holidays 2x because then it is cheap around the clock. Knowing what power and energy your house will consume, you can count the rest. If the house is heated by gas and pump at the same time, it is enough to first calculate how much energy (e.g. per day) came from it, and then calculate the COP based on electricity consumption. The problem will be the gas used for DHW and cooking and electricity for household appliances / RTV, but this can also be avoided. For example, turn off gas appliances and go somewhere for several hours of COP measurement.
* Multiplying by 170 we will obtain an approximate result for the region / season with 3400 heating degree days (e.g. in Białystok). It is much warmer in Wrocław, so you should use e.g. 150 (result for 3000 degrees days) or measure the consumption at the house-environment temperature difference of 15 degrees and multiply by 170 (result for 2550 degrees days). Accurate calculation of energy consumed requires taking into account large differences in the season / region (Fig. 7):
http: //www.info heating.pl/print,id_m-100385